Your character’s attitude and motivation basically define them, so it’s important that you take some time to think about these things in regards to your characters and find the best fit.

Attitude

Let’s start with your character’s attitude. Is your hero a knight in shining armor who thinks people are inherently good, or is he a cynical bastard who thinks it’s in humanity’s nature to destroy itself? Is your villain an unrepentent monster who cares not for the lives of others and is happy to murder them on a whim, or is he a man who believes he’s doing the right thing, even if a few skulls have to be cracked along the way?

A character’s attitude is probably the most important part of who they are, and how they respond to any given situation. Giving your character a compelling attitude will give your audience good reason to like or hate him or her (or both). Just make sure they’re getting the signals you want them to, or you may find the character meant to be a great hero being despised by the audience, or a horrible villain being adored by them, though the latter may happen anyway just by the nature of humanity. For example, some of Metroid’s fanbase love Ridley, despite being a monster of the highest order. (sad fact: despite the fact that Ridley killed Samus’ parents, someone thought it would make sense to write a romantic fanfiction with them pairing up. Wut?)

Motivation

Another important question to ask about your character is his/her motivation, or what drives him/her forward. Is it revenge? Love? The idea of a brighter future? Power? A desire to keep others from being wronged as they were? The fact that Mr. McDoom has taken over, and must be overthrown? Obviously there has to be something driving them or else they wouldn’t be trying to do what it is they’re trying to do.

Motivation, however, is generally one of the easier parts of character creation, as it generally drives whatever plot you have going, though if you think you’re up to it, you can create an alternate motivation, where the main driving force of the story is secondary to your plot, like having your character desire to murder the evil dictator simply because he killed her family, and the fact that she’s saving millions from oppression is just a nice side benefit.